The present invention is directed to an apparatus for sensing the thickness of a pulp suspension course on the forming wire of a paper machine and more particularly, to an apparatus which includes an array of ultrasonic transducers. Lehtinen U.S. Pat. No. 3,442,756 discloses a method of measuring the thickness of pulp suspension being manufactured on the forming wire of a paper machine by the use of an ultrasonic transducer. A single transducer is put under the forming wire of a machine with the water running through the wire acting as an acoustic connector.
With improved high speed actuators for correcting short-term variations in moisture, both in the cross-direction and machine direction of the paper being manufactured, a real time non-scanning wet end sensor is desirable. The Lehtinen sensor, as very cursorily illustrated in the patent, was suitable only for a "probe" operation on a test basis where only a single reading at a time was taken. Also, no scanning of the sensor was suggested, although this is still impractical since a scanning delay cannot be tolerated for correction of short-term variations in moisture and basis weight.